1. Technical Field
The present disclosure relates to microwave surgical devices suitable for use in tissue ablation applications.
2. Discussion of Related Art
Treatment of certain diseases requires the destruction of malignant tissue growths, e.g., tumors. Electromagnetic radiation can be used to heat and destroy tumor cells. Treatment may involve inserting ablation probes into tissues where cancerous tumors have been identified. Once the probes are positioned, electromagnetic energy is passed through the probes into surrounding tissue.
In the treatment of diseases such as cancer, certain types of tumor cells have been found to denature at elevated temperatures that are slightly lower than temperatures normally injurious to healthy cells. Known treatment methods, such as hyperthermia therapy, heat diseased cells to temperatures above 41° C. while maintaining adjacent healthy cells below the temperature at which irreversible cell destruction occurs. These methods involve applying electromagnetic radiation to heat or ablate tissue.
Electrosurgical devices utilizing electromagnetic radiation have been developed for a variety of uses and applications. Typically, apparatus for use in ablation procedures include a power generation source, e.g., a microwave or radio frequency (RF) electrosurgical generator that functions as an energy source and a surgical instrument (e.g., microwave ablation probe having an antenna assembly) for directing energy to the target tissue. The generator and surgical instrument are typically operatively coupled by a cable assembly having a plurality of conductors for transmitting energy from the generator to the instrument, and for communicating control, feedback and identification signals between the instrument and the generator.
There are several types of microwave probes in use, e.g., monopole, dipole and helical, which may be used in tissue ablation applications. In monopole and dipole antenna assemblies, microwave energy generally radiates perpendicularly away from the axis of the conductor. Monopole antenna assemblies typically include a single, elongated conductor. A typical dipole antenna assembly includes two elongated conductors that are linearly-aligned and positioned end-to-end relative to one another with an electrical insulator placed therebetween. Helical antenna assemblies include helically-shaped conductor configurations of various dimensions, e.g., diameter and length. The main modes of operation of a helical antenna assembly are normal mode (broadside), in which the field radiated by the helix is maximum in a perpendicular plane to the helix axis, and axial mode (end fire), in which maximum radiation is along the helix axis.
The particular type of tissue ablation procedure may dictate a particular ablation volume in order to achieve a desired surgical outcome. Ablation volume is correlated with antenna design, antenna performance, antenna impedance, ablation time and wattage, and tissue characteristics, e.g., tissue impedance.
Because of the small temperature difference between the temperature required for denaturing malignant cells and the temperature normally injurious to healthy cells, a known heating pattern and precise temperature control is needed to lead to more predictable temperature distribution to eradicate the tumor cells while minimizing the damage to otherwise healthy tissue surrounding the tissue to which electrosurgical energy is being applied. Fluid-cooled or dielectrically-buffered microwave devices may be used in ablation procedures. During operation of the microwave ablation device, if the flow of coolant or buffering fluid is interrupted, the microwave ablation device may exhibit rapid failures due to the heat generated from the increased reflected power.